Various polymeric hard gas permeable contact lenses are known. Siloxane based materials often are prepared by copolymerization of a siloxanyl alkyl ester of methacrylic acid with other acrylate or methacrylate monomers in many known formulations. Such compositions can exhibit excellent oxygen permeability but often have less than desired biocompatibility sometimes due to their hydrophobic nature.
The art has attempted to impart hydrophilic properties to such siloxane systems through the incorporation of wetting agents or surface modification of finished lenses. Certain wetting agents can lead to accumulation of proteinaceous matter from tear fluid which can result in decreased transparency and wearer discomfort. Surface modification or treatment can also increase wettability but often such treatments are subject to lack of permanence.
The art has recognized that introducing fluorine-containing groups into contact lens polymers can significantly increase oxygen permeability. Contact lens compositions based on fluoroalkylacrylates or methacrylates are known to the art. These materials range from soft to semi-rigid and often require the use of special wetting agents or surface treatments.
Contact lenses based on telechelic perfluorinated polyethers have recently been made public. Such lenses are reported to be highly oxygen permeable and resistant to adsorption of tear components but can be relatively soft making it difficult to use conventional machining techniques known to the art.
Polymeric compositions containing both organosiloxane and fluorinated components are also known. U.S. Pat. No. 4,433,125 discloses copolymers formed of polymerizable organosiloxanes and fluoroalkylacrylates and methacrylates. Some of the materials disclosed have high oxygen permeability but are not believed to simultaneously exhibit levels of hardness desired to fully exploit the advantages of rigid hard gas permeable contact lenses.
Other prior art as in U.S. Pat. No. 4,486,577 has sought to find specific polysiloxanes which are particularly suitable for use in contact lenses. In some cases such as in U.S. Pat. No. 4,486,577, where a specifically designed polysiloxane found to be suitable for contact lens use is disclosed, the developers have indicated that various compounding comonomers can be used including fluoro-containing materials such as itaconates. However, such prior art has not recognized that known and commercially used organosiloxanes in various combinations can have their oxygen permeability increased in contact lens formulations by the addition of fluorinated itaconates.
For example, one particularly well known formulation for contact lens use is that found in U.S. Pat. No. 4,152,508 where various esters of itaconates have been shown to be useful in providing desirable contact lens properties with desired low hydration values and high oxygen permeability coupled with excellent wetting properties and good hardness and dimensional stability. However, oxygen permeability of such materials has often been limited to a value less than DK35.